Abstract: By substituting low purity neodymium for the high purity one, NdFeB permanent magnets of (BH)_max=41 MGOe were prepared by powder metallurgy. Several properties of NdFeB alloys were measured by means of x-ray diffraction, the differential thermal analyzer, magnetic balance, extracting sample magnetometer and pulse high magnetic field apparatus respectively. The results show that there is a peak of phase transition at 1439K, and the abnormal phenomenon on the magnetic hysteresis loop at low temperature originates from the conical magneto-crystalline anisotropy of the major phase Nd₂Fe₁₄ in the NdFeB alloys.